System And Methods For Efficient Authentication Of Medical Wireless Ad Hoc Network Nodes

ABSTRACT

A medical ad hoc wireless network ( 10 ) is deployed in a healthcare medical facility surrounding individual patients and including wireless nodes (A, B, . . . , Z). Before deployment, each node (A, B, . . . , Z) is pre-initialized with a public key certificate ( 22 ) and offers a trust and symmetric key distribution service ( 32 ). In joining the ad hoc network ( 10 ), a node (B) authenticates and registers to one randomly self-chosen node (A) by using certified public keys ( 20 ). Such node (A) becomes Trusted Portal (TP A ) of the node (B). The node (B) dynamically registers to a new self-chosen TP node when its old TP node leaves the ad hoc network ( 10 ). The network ( 10 ) supports symmetric key authentication between nodes registered to the same TP node. Additionally, it supports symmetric key authentication between nodes registered to different TP nodes.

DESCRIPTION

The present invention relates to the security in the network systems and methods. It finds particular application in conjunction with medical wireless ad hoc network systems and will be described with particular reference thereto. However, it is to be appreciated that the invention will also find application in conjunction with other short-range network systems and the like.

Typically, wireless mobile ad hoc networks are deployed in hospitals and medical facilities for medical patient care and monitoring. Commonly, a medical mobile ad hoc network is established around a patient or a small group of patients. In the medical mobile ad hoc network, medical devices communicate peer-to-peer. Each device offers a set of medical services and demands access to a set of medical services on other devices. The access to such devices is also given to the clinicians who, for example, using a PDA can trigger an infusion pump to administer morphine to a patient.

It is essential to ensure that only the right entities access medical mobile ad hoc networks, and to ensure confidentiality and integrity of wireless communications. In the example discussed above, the doctor can trigger an infusion pump to administer morphine to a patient, but a patient's visitor must be restrained from such an act.

Entity authentication is the basis for subsequent access control and establishment of protected communication. Entity authentication protocols, which are typically used in infrastructure networks, are based on either public key or symmetric key cryptography. However, these protocols are not suitable for mobile ad hoc networks. In a public key cryptography authentication protocol, a node A validates a node's B knowledge of the private key associated to node's B public key. Node's B public key must be certified and associated to node's B identity by a trusted third party (TTP) common to A and B. Public key cryptography involves a great deal of computational power. Studies show that an RSA private key encryption takes about eighteen seconds on a 133 MHz handheld. Consequently, with moderate computing-power devices employed by the ad hoc network systems, the user's access to the services is delayed and battery resources are exhausted. The problem with typical symmetric key cryptography authentication protocols resides in the absence of online infrastructure support. Therefore, an online trusted third party (TTP) is not available to distribute common symmetric keys to two authenticating nodes. An alternative solution is the pre-distribution of identity-labeled pair-wise symmetric keys to all mobile nodes before deployment. However, symmetric key cryptology is limited in scalability and security administration. Key management is vastly complicated, e.g. when updating a key in one of the nodes or adding a new node, the rest of nodes must also be updated to share a key with the new node. There are many pairs of keys to be managed. The management of the system with a large population of nodes can become practically infeasible since the storage requirements of the system grow as N².

Accordingly, there is a need for an efficient authentication system suitable for low power mobile devices. The present invention provides a new system and methods which overcome the above-referenced problems.

In accordance with one aspect of the present invention, a security system for an ad hoc wireless network is disclosed. The security system comprises a plurality of local wireless network nodes. A means distributes trust and symmetric keys among the ad hoc network nodes.

In accordance with another aspect of the present invention, a method of key management is disclosed. Trust and symmetric keys are distributed among nodes of an ad hoc network.

One advantage of the present invention resides in providing computationally efficient authentication protocols suitable for low-computing power and battery powered mobile devices.

Another advantage resides in an authentication system without requiring online support from infrastructure network or central servers.

Another advantage resides in node authentication based on certified node identities regulated by an administrative entity.

Another advantage resides in distributing the symmetric keys within the ad hoc network without the need to contact external key distribution servers.

Another advantage resides in random and dynamic distribution of key distribution functionality among ad hoc network nodes. Therefore, the availability and robustness of the security system is optimized.

Another advantage resides in secure distribution of security material, patient data and other confidential information.

Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

FIG. 1 is a diagrammatic illustration of an ad hoc wireless network;

FIGS. 2A-B diagrammatically show a first mobile node of the ad hoc network establishing a trust relationship with a first trusted portal and creating a first TP-domain;

FIG. 3 is the illustration of functional blocks of a portion of the ad hoc wireless network;

FIGS. 4A-B diagrammatically show a second mobile node of the network system establishing a trust relationship with the same first trusted portal and joining the first TP-domain;

FIGS. 5A-B diagrammatically shows a first mobile node establishing a trust relationship with a second mobile node when both nodes belong to the same TP-domain;

FIG. 6 is the illustration of functional blocks of another portion of the ad hoc wireless network;

FIGS. 7A-B diagrammatically show a first mobile node establishing a trust relationship with a second mobile node when both nodes belong to different TP-domains; and

FIG. 8 is the illustration of functional blocks of another portion of the ad hoc wireless network.

With reference to FIG. 1, each short-range ad hoc wireless network 10 includes mobile nodes (A, B, . . . , Z) owned by a single administrative entity, e.g. a hospital, an enterprise, a factory, or the like. Typically, each ad hoc network 10 includes from ten to twenty self-organized nodes (A, B, . . . , Z) which are connected by wireless single-hop links with no fixed network infrastructure support. Preferably, the mobile nodes (A, B, . . . , Z) include physiological monitoring devices, controlled medication administration devices, PDA-like devices, embedded computing systems, or the like devices which have moderate computing power. Preferably, a number of independent short-range ad hoc networks 10 are spread randomly in a well-limited deployment area. The wireless coverage area of each ad hoc network 10 ranges for up to forty meters, extending thus often beyond the deployment area. For example, one network may include nodes for each physiological monitor, medication administration device, computer-based patient ID, attending physician's PDA, and the like, but specifically excluding like devices associated with other patients.

Preferably, new nodes (A, B. . . . , Z) join or leave any of the ad hoc networks 10 sporadically, i.e., the topology of the network 10 is unknown a priori. Preferably, the nodes are in a communication range to perform security mechanisms without undesired interruptions. Each mobile node (A, B, . . . , Z) offers one or more network services. Each node (A, B, . . . , Z) can communicate peer-to-peer with any other node in the network system 10 via transmitting/receiving means 14 to access one or more services. Peer-to-peer communications is preferably unidirectional and bidirectional and can be synchronous and asynchronous. Of course, it is also contemplated that a physician can access the node (A, B, . . . , Z) to provide a service to the patient, e.g. administer a medication, check a status of the monitoring equipment, and the like, by using a portable computer, PDA, or the like.

Preferably, the nodes (A, B. . . . , Z) are tamper-proof protected, so no information can be learnt tampering them. Furthermore, the nodes (A, B, . . . , Z) of the network system 10 behave properly and do not issue false assertions or statements.

Initially, before deployment of the nodes (A, B, . . . , Z), the nodes (A, B, . . . , Z) are initialized with security material of a Public Key Infrastructure (PKI) operating with an offline certification authority (CA) (not shown). In a secure perimeter, the offline CA issues a digital public key certificate, a private key and a CA's public key to each node (A, B, . . . , Z). Each public key certificate binds a certified unique node's identity with its corresponding public key. Each node (A, B, . . . , Z) securely holds its private key 18, the CA's public key 20, and the public key certificate 22 in a security database 24.

The nodes (A, B, . . . , Z) can act both as local security servers and as security clients within the ad hoc network 10. As a security client, a node can take the role either of a supplicant or of an authenticator. In a node-to-node communication, the supplicant is a node that demands access to a second node. The authenticator is the second node, which needs to verify the accessing node's identity. As a security server, a node takes the role of Trusted Portal (TP). A trusted portal offers an online trusted third party service to the trusted nodes in its TP-domain as will be discussed in a greater detail below.

The security system is based on cooperation of the nodes and unconditional trust of the node to the TP given that all nodes belong to the same administrative (or PKI) domain and that physical security safeguards are deployed.

With continuing reference to FIG. 1 and further reference to FIGS. 2A-B and 3, each node (A, B, . . . , Z) includes a Key Management means or center or process 32 _(A), 32 _(B), . . . 32 _(Z), which provides trust establishment among the nodes (A, B, . . . , Z) and distribution of long-term symmetric keys to enable the nodes (A, B, . . ., Z) to authenticate each from that moment on. A trust initialization means or process 34 _(A), 34 _(B) enables a node B, unknown to a node A, to set up a trusted portal (TP) in the ad hoc network 10 by arbitrarily self-choosing the node A as its trusted portal and sending a service request to the node A.

More specifically, the node B trust initialization means 34 _(B) issues a service request to the node A trust initialization means 34 _(A). A node authentication means 36 _(A) of the node A authenticates the node B by using the CA's public key 20 _(A), the node's B public key certificate 22 _(B) and the node's B private key 18 _(B). Such authentication is well known in the art. (See, for example, The Handbook of Applied Cryptography, by A. Menezes, P. Van Oorschot and S. Vanstone, CRC Press, 2001.) Next, the node authentication means 36 _(B) of the node B authenticates the node A by a use of the CA's public key 20 _(B), the node's A public key certificate 22 _(A) and the node's A private key 18 _(A). Once the nodes A and B mutually authenticate each other using certified public keys 20 _(A), 20 _(B), the node B sets the node A as its trusted portal TP_(A), and a session key is derived.

A symmetric key computing means 38 _(A) calculates a long-term symmetric key K_(AB) that allows the node A to identify a registered node B from now on. The symmetric key K_(AB) is also used for protecting the contents of messages in next communications between the nodes A and B. The calculation of the symmetric key K_(AB) is based, for example, on the calculation of shared keys for Lotus Notes Session Resumption, well known in the art. E.g., the symmetric key computing means 38 _(A) computes the key K_(AB) by calculating the hash of the concatenation of a long term self-calculated secret S_(A) known only to the node A, with the node's B identity ID_(B): K _(AB) =h(S _(A) , ID _(B)). The hash algorithm is well known in the art. E.g., a hash function h(m) is a one-way mathematical transformation that takes a message m of an arbitrary length and computes from it a fixed-length short number h(m). Given m, computing h(m) is relatively easy. Given h(m), computing m is computationally infeasible. In addition, it is computationally infeasible to get two messages m1 and m2 with the same h(m).

With continuing reference to FIG. 3, an encrypting means 40 _(A) encrypts and integrity protects the symmetric key K_(AB). A key distributing means 42 _(A) sends the encrypted symmetric key K′_(AB) using the session key to the node B. A node B decrypting means 44 _(B) decrypts the encrypted key K′_(AB).

The symmetric key K_(AB) is stored in corresponding symmetric key memories 46 _(A), 46 _(B). From now on, the node B is registered as a trusted node with the node A.

In one embodiment, the node A does not store the symmetric key K_(AB) but only the secret S_(A) in a secret memory 48 _(A). The node A can recalculate the key K_(AB) anytime from the secret S_(A) and the node's B identity ID_(B), which is provided by the node B during the trust initialization process. A compromise of the node A security database 24 _(A) does not reveal any information about the registered node B. The storage requirements are kept constant, not depending on the number of the registered nodes.

The node B can establish an initial trust with whatever node it chooses within the ad hoc network 10. The initialization process 34 _(A), 34 _(B) requires the nodes A, B to have only moderate computing power and valid public key certificates.

With reference again to FIG. 21, as a result of the trust initialization, authentication and symmetric key distribution, a node A TP-domain D_(A) is created, containing the node B as the trusted node, i.e. D_(A)={ID_(B)}. The trusted portal TP_(A) vouches for the identity of a trusted node B to other trusted nodes.

With reference to FIGS. 4A-B, although initially the node A is not a trusted portal of any other node in the network system 10, after initial trust establishment by the node B, the node A can also serve as the trusted portal TP_(A) to other nodes in the network system 10. All the nodes, that set trust with the TP_(A), form TP-domain D_(A) of the node A. E.g., the TP-domain D_(A) grows when a node C sets initial certified trust to the node A and obtains a shared symmetric key K_(AC). The node A is the TP-domain administrator of its own TP-domain D_(A), i.e. the node A decides when to accept a node in its TP-domain D_(A) or when a trust relationship expires.

With reference again to FIG. 3, a de-registration means or process 50 _(A) enhances security by regulating the lifetime of the node A TP-domain D_(A) by the life cycle of the secret S_(A), i.e. the time the node A holds the same value of the secret S_(A). After a prespecified period of time T₁, the de-registration means 50 _(A) nullifies the value of a current secret S¹ _(A) by calculating a random number R which becomes a second secret S² _(A). As a result, all previous established trusted nodes are automatically de-registered. E.g., when the secret value S¹ _(A) is changed to S² _(A), the symmetric key K_(AB), which has been previously distributed to the node B, does not match S² _(A) and, thus, is not a valid shared-key to authenticate the node B to the node A. This makes the node B newly unknown node to the node A. Preferably, the de-registration process 50 _(A) is performed anytime when the trusted portal TP_(A) moves away from the ad hoc network 10. After the deregistration, the above-described registration is repeated to build a new TP-domain. Particularly, if the node A has left the network 10, one of the other nodes assumes the central responsibility.

With reference to FIGS. 5A-B and 6, the trusted portal TP_(A) acts as an online trusted third party by securely distributing a shared symmetric key K_(BC) to the nodes B and C, which are members of the TP-domain D_(A) that share corresponding symmetric keys K_(AB), K_(AC) with the node A. An intra-domain trust and key distribution (ITKD) means or process or protocol 52 _(A) allows the reference node A to send a key associated to the identity of the trusted node B to another trusted node C when both nodes B, C are included in the trusted TP-domain D_(A).

More specifically, the node B trust initialization means 34 _(B) sends to a node C trust initialization means 34 _(C) a request for access. The node C trust initialization means 34 _(C) determines that the node B belongs to the same TP-domain D_(A) of the trusted portal TP_(A). A node C intra-domain means 52 _(C) communicates to a node B intra-domain means 52 _(B) that the node C belongs to the same TP-domain D_(A).

The intra-domain means 52 _(B) of the node B contacts the intra-domain means 52 _(A) of the trusted portal TP_(A) and requests a symmetric key to the node C. The request is encrypted under the key K_(AB) to guarantee the confidentiality of the process and the anonymity of the trusted portal TP_(A). The symmetric key computing means 38 _(A) of the node A generates a random authentication symmetric key K_(BC) for the nodes B, C which is encrypted and distributed to the nodes B, C. More specifically, a node A encrypting means 40 _(A) encrypts and integrity protects the key K_(BC) and the node's C identifier ID_(C) with the key K_(AB). The key distributing means 42 _(A) sends the encrypted key K′_(BC) to the node B. Next, the node A encrypting means 40 _(A) encrypts and integrity protects the key K_(BC) and the node's B identifier ID_(B) with the key K_(AC). The node A key distributing means 42 _(A) sends the encrypted key K″_(BC) to the node C. Alternatively, to optimize the efficiency of the ITKD process, the supplicant or the node B triggers the ITKD process 52 _(A) and the trusted portal TP_(A) communicates exclusively with the node B. The key distributing means 42 _(A) distributes the encrypted keys K′_(BC), K″_(BC) to the node B. A node B key distributing means 42 _(B) forwards the encrypted key K′_(BC) to the node C. Corresponding decrypting means 44 _(B), 44 _(C) decrypts the encrypted keys K′_(BC), K″_(BC). The shared symmetric key K_(BC) is stored in corresponding symmetric key memories 46 _(B), 46 _(C). A node C authentication means 36 _(C) uses the symmetric key K_(BC) to authenticate the node B. Of course, it is also contemplated that the node B authentication means 36 _(B) can authenticate the node C by a use of the symmetric key K_(BC).

The nodes B, C will not accept a key distributed by the node A if the nodes B, C do not have an established relationship with the node A. Likewise, the node A does not directly distribute keys to unknown nodes, i.e. to the nodes not belonging to the node A TP-domain D_(A).

The trust initialization process 32 is utilized every time a new node joins the ad hoc network 10 or a trusted portal disappears. For instance, if the trusted portal TP_(A) leaves the ad hoc network 10, the nodes B and C need to establish a new trusted portal. Establishing trust among the nodes (A, B, . . . , Z) of the ad hoc network 10 in this manner, a random path of trusted portals interconnects all the nodes (A, B, . . . , Z) in the ad hoc network 10. As will be discussed in a greater detail below, cooperation among different trusted portals enables vouching for the nodes trusted by different trusted portals. The trusted portals of different TP-domains coordinate to act as trusted third parties by securely distributing a common symmetric key to nodes in different TP-domains.

With reference to FIGS. 7A-B and 8, a cross-domain trust means or protocol or process 60 _(A), 60 _(B), 60 _(D), 60 _(E) enables two or more trusted portals TP_(A), TP_(D) to send a key associated to the identity of the node B included in the TP-domain D_(A) of the trusted portal TP_(A) to a node E included in a TP-domain D_(D) of the trusted portal TP_(D), e.g. a node D, which is a trusted node of the node A which has been already initialized as explained above.

More specifically, the node B trust initialization means 34 _(B) sends to a node E trust initialization means 34 _(E) a request for access. The node E trust initialization means 34 _(E) determines that the node B belongs to a different TP-domain. The node E cross-domain means 60 _(E) communicates to the node B cross-domain means 60 _(B) that the node E belongs to a different TP-domain. Preferably, the node E cross-domain means 60 _(E) communicates to the node B cross-domain means 60 _(B) that the node E belongs to the TP-domain D_(D) of the trusted portal TP_(D). Since the trusted TP-domains build hierarchically, two different trusted portals are interconnected by either a direct trust relationship or by a set of them. In one embodiment, the cross-domain means 60 _(A) determines the shortest path to a target node.

The node B cross-domain trust means 60 _(B) contacts the cross-domain trust means 60 _(A) ofthe trusted portal TP_(A) and requests a key to communicate to the node E. The request is encrypted under the key K_(AB) to guarantee the confidentiality of the process and the anonymity of the trusted portal TP_(A). The node A symmetric key computing means 38 _(A) randomly generates a new authentication symmetric key K_(BE) for the nodes B, E. The encrypting means 40 _(A) encrypts and integrity protects the key K_(BE) and the node's E identifier ID_(E) with the key K_(AB). The key distributing means 42 _(A) sends the encrypted key K′_(BE) to the node B. Next, the encrypting means 40 _(A) encrypts the key K_(BE) and the node's B identifier ID_(B) with the key K_(AD). The key distributing means 42 _(A) sends the encrypted key K″_(BE) to the trusted portal TP_(D). A node D decrypting means 44 _(D) decrypts the encrypted key K″_(BE) to obtain the key K_(BE). A node D encrypting means 40 _(D) encrypts and integrity protects the key K_(BE) by using the key K_(DE). A node D key distributing means 42 _(D) forwards the encrypted key K″′_(BE) to the node E. In one embodiment, the key distributing means 42 _(A) securely forwards the encrypted keys K′_(BE), K″_(BE) to the node D. The node D decrypting means 44 _(D) decrypts the encrypted key K″_(BE) to obtain the key K_(BE). The node D encrypting means 40 _(D) encrypts and integrity protects the key K_(BE) by using the key K_(DE). The key distributing means 42 _(D) forwards the encrypted keys K′_(BE), K″′_(BE) to the node E. A key distributing means 42 _(E) of the node E forwards the encrypted key K′_(BE) to the node B. Corresponding decrypting means 44 _(B), 44 _(E) decrypts the encrypted keys K′_(BE), K″′_(BE). Using the symmetric key K_(BE) as an authentication protocol, a node E authentication means 36 _(E) authenticates the node B. Alternatively, the node B authentication means 36 _(B) authenticates the node E. The symmetric key K_(BE) is stored in corresponding symmetric key memories 46 _(B), 46 _(E) of the corresponding nodes B, E.

The cross-domain trust process works similarly for a larger number of intermediate trusted portals.

In one embodiment, to protect against replay attacks, the encrypted messages are additionally integrity protected, e.g. by including timestamps or periodically regenerating encryption keys and re-establishing the network.

The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. 

1. A security system for an ad hoc wireless network comprising: a plurality of local wireless network nodes; and a means for distributing trust and symmetric keys among the local wireless network nodes.
 2. The system as set forth in claim 1, further including: a trust initialization means for establishing a trust relationship among the network nodes of the ad hoc network.
 3. The system as set forth in claim 2, wherein the trust initialization means establishes a trust relationship between a first and a second node, wherein the first node is arbitrarily selected by the second node from the network nodes to be a trusted portal of the ad hoc network and further including: an authentication means for performing an authentication between the first node and the second node; and a symmetric key means for computing a symmetric key which establishes a long-term trust relationship between the trusted portal and the second node.
 4. The system as set forth in claim 3, wherein the authentication is mutually performed by a use of certified public keys which are issued to the first and second nodes by an offline certification authority preceding the establishment of the trusted portal.
 5. The system as set forth in claim 3, wherein the tust relationship means establisies a trust relationship between the first node and one or more nodes such that a TP-domain of the trusted portal grows.
 6. The system as set forth in claim 3, further including: an intra-domain trust and key distribution means for distributing trust information to two or more nodes that have previously established the trust relationship with the trusted portal.
 7. The system as set forth in claim 6, wherein, in response to a request by the second node, the symmetric key computing means calculates a symmetric key associated to the identities of the two or more nodes.
 8. The system as set forth in claim 7, wherein authentication means uses the calculated symmetric key (K_(BC)) to mutually authenticate the two or more nodes.
 9. The system as set forth in claim 3, further including: a cross-domain trust and key distribution means for distributing trust information to two or more nodes that have previously established trust relationships with different corresponding trusted portals.
 10. The system as set forth in claim 9, wherein, in response to a request to the trusted portal by the second node, the symmetric key computing means calculates a symmetric key which is associated to the identities of the two or nodes and which key is sent securely encrypted from the trusted portal to the second node, and another of the two or more nodes via at least the trusted portal.
 11. The system as set forth in claim 10, wherein authentication means uses the symmetric key to mutually authenticate the two or more nodes.
 12. The system as set forth in claim 1, further including: a plurality of devices including at least one of physiological condition monitors, controllable medication dosing devices, and PDAs, each device being associated with one of the network nodes.
 13. A method of key management comprising: distributing trust and symmetric keys among nodes of an ad hoc network.
 14. The method as set forth in claim 13, further including: establishing a first trusted portal which is arbitrarily selected from the nodes of the network by a first node; performing an initial authentication between the first trusted portal and the first node; and computing a symmetric key which establishes a long term trust relationship between the first trusted portal and the first node.
 15. The method as set forth in claim 14, wherein the step of authentication includes: performing the authentication by a use of certified public keys which have been issued to each node of the ad hoc network by an offline certification authority preceding the establishment of the trusted portal.
 16. The method as set forth in claim 14, further including: distributing the symmetric key between nodes that have previously established trusted relationships with the same trusted portal.
 17. The method as set forth in claim 16, further including: in response to a request by the first node, computing a symmetric key associated to the identities of the nodes that previously established trust relationship; and authenticating the nodes that previously established trust relationships with the calculated symmetric key.
 18. The method as set forth in claim 14, further including: distributing the symmetric key between a second set of nodes that have previously established trust relationships with different corresponding first and second trusted portals.
 19. The method as set forth in claim 18, further including: in response to a request to the first trusted portal by the first node, computing a symmetric key; sending the symmetric key from the first trusted portal to the first node which symmetric key is securely encrypted and integrity protected; sending the symmetric key from the first trusted portal to the second trusted portal which symmetric key is securely encrypted and integrity protected; sending the symmetric key from the second trusted portal to the second of the second set of nodes that previously establish trust relationships which symmetric key is securely encrypted and integrity protected; and authenticating the second set of nodes and with the symmetric key.
 20. A network having a plurality of nodes programmed for performing the method of claim
 13. 